Spark plug boot



R. C. WOOFTER SPARK PLUG BOOT Jan. 12, 1954 Filed Oct. 30, 1952 IN VENTOR. 305E117 6. N00fTfH HIS ATM/"([18 Patented Jan. 12, 1954 SPARK PLUGBO-OT Robert C. Woofter, Cortland, Ohio, assignor to General MotorsCorporation, Detroit, Mich., a corporation of Delaware ApplicationOctober 30, 1952, Serial No. 317,658

Claims.

This invention relates to spark plug boots or shields, which aredesigned'to enclose parts of installed spark plugs and also theconnections through the medium of which the lead in wires areelectrically connected to the plugs. Boots of this general character arewell known and the purpose thereof is to prevent short circuiting andother difliculties by protecting the plug and electrical connectionsfrom moisture, oil, soot and dirt.

The primary purpose of the present invention is to provide a novel sparkplug boot such as described which is universal in character, that is, aboot which can be readily assembled in position on the plug andassociated lead in wire, whether the latter is in substantial alignmentwith the plug or lies at an angle to the plug,

A further object of the invention is to provide a boot of this characterwhich can be readily flexed to accommodate itself to the position of theplug and lead in wire, but which fits tightly on the plug and lead inwire and is of sufficient rigidity at such points to prevent any leakageof water or passage of dirt into the space within the boot.

According to the present invention, these objects are accomplished byproviding a boot which is generally cylindrical in form, is ofconsiderable rigidity at one end where the boot engages the spark plug,is of reduced diameter at the opposite end to have a tight fit with thelead in wire and is somewhat thickened at the point of engagementtherewith so as not to stretch. The intermediate portion of the bootbetween the end portions above referred to is relatively thin and iscorrugated as is the wall of a bellows and is of such a size that itsinterior wall is spaced somewhat from the lead in wire and theconnecting means through which the wire is connected to the plug, sothat the boot can be readily flexed to accommodate a plug and lead inwire which are in substantial alignment or which are arranged atsubstantially any angle to each other.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

In the drawings:

Figure 1 is an elevation of the boot which forms the subject of thisinvention associated with a plug and lead in wire at a 90 angle to eachother;

Figure 2 is a similar elevation showing the lead in wire and plug inalignment;

Figure 3 is a section on the line 33of Figure.

2; and

Figure 4 is a view of the boot alone seen in the direction of the arrowin Figure 3.

As shown in the drawings, the usual outer metal shell of the spark plugwhich is screwed into the engine cylinder head is designated 5, whilethe insulator which extends upwardly therefrom and surrounds the centralelectrode 2 is designated 3. The electrode 2 cooperates in the usual waywith the electrode d which is integral with the threaded part of themember I and extends inwardly toward electrode 2 in the manner wellknown.

The electrode 2 is connected at its upper end with a terminal member 5shown in dotted lines in Fig. 3 which extends above the insulator 3 inposition to be engaged by a terminal clip 8 which is connected in anydesirable way to the lead in wire 1 and surrounds the outer surface ofthe insulation 8 which covers such lead in wire. The types of lead interminals on the plug and connecting wire are purely conventional, arenot material, so far as this invention is concerned, and any suitableform of connecting means can be used.

The protecting boot is indicated generally at it and comprises threesections numbered l i, [2 and I3. The first of these sections is adaptedto fit on the insulator 3 the outer surface of which is slightlytapered, and the boot is adapted to be pushed down on the insulatoruntil a narrow shoulder M on the inner surface of the boot engages thetop of the insulator as indicated in Fig. 3. In this position, the boothas a tight lit with the surface of the insulator to prevent admissionof moisture or dirt between the insulator and the boot and whenassembled, the boot, at the lower edge thereof is slightly stretched sothat the boot grips the insulator with considerable pressure, thepressure being suflicient to prevent any movement of the boot relativeto the insulator unless considerable force is applied thereto.

It will be noted particularly that the part I l of the boot whichsurrounds the insulator 3 has a wall of considerable thickness, morethan double that of the balance of the boot, and is relativelynon-resilient by comparison with other parts of the boot so that a veryappreciable force is required to stretch this part of the boot as itforced on the insulator. Thus, the boot is caused to grip the insulatorwith considerable force, as previously described. The part H of the bootis provided with a series of circumferential ribs 15 which enable theboot to be better gripped by the assembler when it is forced on the plugand the shoulder l4 constitutes a means for properly locating the bootwhen it is positioned on the plug The upper part l3 of the boot iscylindrical throughout most of its length and is of such size that it isspaced from the outer surface of the insulation 8 which covers the leadin wire I. At the extreme upper end of the part E3 of the boot it isthickened as indicated at [6, forming a sort of annular flange the innerdiameter of which is so reduced that it has a tight enough fit with theinsulation 8 to prevent admission of moisture and dirt between suchflange and the insulation.

Th portion l2 of the boot which lies between the parts H and i3. is ofsubstantially the same wall thickness as the cylindrical portion of part!3, is spaced from the covering of the lead in wire and from theconnector terminal 5, and is corrugated as best shown in Fig. 3 so thatit can be very easily bent as desired. In other words, this part of theboot is, in effect, a bellows and therefore is exceedingly flexible. Thespacing between the wall and the elements inside it permit flexing ofthe boot to be effected without material interference brought about byengagement of the boot with the parts which are surrounded thereby.

In some installations the lead in Wires are so arranged that they are insubstantial alignment with the plugs as indicated in Fig. 2, while inother installations the terminal 6 is bent and the lead in wires arearranged at an angle with respect to the plug, either a right angle asindicated in Fig. 1, or some other angle. The boot which forms thesubject of this invention is so easily flexed that it can be used withany installation, either such an arrangement as shown in Fig, 2, or inany installation where the lead in wire and the plug are not inalignment without disturbing the tight fit of the boot with both thelead in conductor and the plug.

The specific material from which the boot is made is not a part of thepresent invention, although the material used must be resistant to theeiiects of heat, oil and other deteriorating efiects and substances.Various substances might be employed, for example, natural rubber,synthetic rubber compounds, or a plastic such as Vinylite. However, ithas been found that a synthetic rubber such as neoprene probably givesbetter results than either natural rubber or a plastic such as referredto because the adverse eiTect of heat and the corona action resultingfrom high voltage is less with a neoprene compound than with the othermaterials mentioned. For example, the eifect of corona action is greaterwith natural rubber than with neoprene. Heat does not cause it to becomebrittle as a vinyl plastic will in time when exposed to the effect ofheat. Moreover, the neoprene compound is highly oil-resistant.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. The combination with a spark plug having means for securing the plugin the cylinder block of an engine, an insulator element supportedthereby and having a connector terminal mount- 7 rounding said terminalsand having a part adapted to fit tightly on said insulator element whenthe casing is in proper position, said part having a relativelynon-elastic wall of substantial thickness, a second part adapted to fittightly on the conductor element and an intermediate part havin acorrugated and relatively thin wall surrounding and spaced from saidterminal elements, said intermediate part being freely flexible topermit universal bending of the protective shield, so that said shieldcan be used with spark plug assemblies where the conductor element is inalignment with the plug or at an angle thereto.

2. ihe combination with a spark plug having means for securing the plugin the cylinder block of an engine, an insulator element supportedthereby and having a connector terminal mounted thereon, and anelectrical conductor having a terminal on one end adapted to engage saidfirst-mentioned terminal, of a protecting shield adapted to preventaccess of dirt and moisture comprising a casing of insulatin materialsurrounding said terminals and having a part adapted to fit tightly onsaid insulator element when the casing is in proper position, and havinga relatively non-elastic wall of substantial thickness, a second partspaced from the conductor and having an inwardly projecting flangeadapted to fit tightly on the surface of said conductor, and anintermediate part having a corrugated and relatively thin wallsurrounding and spaced from said terminal elements, said intermediatepart being freely flexible to permit universal bending of the protectiveshield, so that shield can be used with spark plug assemblies where theconductor element is in alignment with the plug or at an angle thereto.

' 3. The combination with a spark plug having means for securing theplug in the cylinder block of an engine, an insulator element supportedthereby and having a connector terminal mounted thereon, and anelectrical conductor having a terminal on one end adapted to engage saidfirstmentioned terminal, of a protecting shield adapted to preventaccess of dirt and moisture comprising a casing of insulating materialsurrounding said terminals and having a part engaging said insulatorelement with a wall thickness at least substantially double the wallthickness of the remainder of the casing, said thick walled portion ofthe casing having at least partial external circumferential ribs formedthereon, and said casing having an annularly corrugated part surroundingand spaced from said terminal elements and adjacent said thick walledportion, said last-named part being freely flexible to permit universalbending of said last-named part of the casing.

4. The combination with a spark plug having means for securing the plugin the cylinder block of an engine, an insulator element supportedthereby and having a connector terminal mounted thereon, and anelectrical conductor having a terminal on one end adapted to engage saidfirst-mentioned terminal, of a protecting shield adapted to preventaccess of dirt and moisture comprisin a casing of insulating materialsurrounding said terminals and having a part engaging said insulatorelement with a wall thickness of at least substantially double the wallthickness of the remainder of the casing, said thick walled portion ofthe casing having external circumferential ribs formed thereon, saidcasing having another part surrounding and spaced from said terminalelements and adjacent said thick walled portion, said last-named partbeing corrugated and freely flexible to permit universal bending of saidlast-named part of the casing, and a third part of the casingsurrounding the conductor and spaced therefrom throughout most of itslength, said last-named part having an internally extending flangeadapted to engage the outer surface of said conductor.

5. For use with a spark plug adapted to be secured in the cylinder blockof an engine and having an insulator element supported thereby and aconnector terminal mounted thereon which is adapted to be engaged by aterminal on one end of an electrical conductor associated with saidspark plug; a protective boot adapted to prevent access of dirt andmoisture comprising a casing of insulating material surrounding saidterminals and having a part adapted to fit tightly on said insulatorelement when the casing is in proper position, said part having arelatively non-elastic wall of substantial thickness, a second partadapted to fit tightly on the conductor element and an intermediate parthaving a corrugated and relatively thin wall surrounding and spaced fromsaid terminal elements, said intermediate part being freely flexible topermit universal bending of the protective boot, so that said boot canbe used with spark plug assemblies where the conductor element is inalignment with the plug or at an angle thereto.

ROBERT C. WOOF'IER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,376,844 Weber May 3, 1921 1,898,064 Ridge Feb. 21, 19 32,033,360 St. Clair Mar. 10, 1936 2,468,225 Murphy Apr. 26, 1949

